Optical circulator

Abstract

A polarization independent optical circulator is disclosed. A first birefringent plate (10) is used to separate an incident beam from a first port into two beams having orthogonal polarizations, and a second plate (11) recombines the beams at a second port. Means (12) providing nonreciprocal rotation of the polarizations are disposed between the plates. Placed between the rotating means and the second plate is a third plate (16) to further separate the beams and a reflecting element (17) for deflecting the beams toward the second port. The reflecting element includes a slotted portion (18) so that light from a third port can pass therethrough back toward the first port.

What is claimed is: 
     
       1. An optical circulator having at least three ports comprising: a first birefringent plate disposed at a first port in order to separate an incident light beam at that port into two beams having orthogonal directions of polarization;   a second birefringent plate disposed at a second port in order to recombine the two beams;   means disposed between the plates for nonreciprocal rotation of the directions of polarization of the beams;   a third birefringent plate disposed between the rotation means and the second plate for further separating the two beams; and   a reflecting element disposed between the third plate and second plate for deflecting the two beams toward the second port, the said element having a slot which permits passage therethrough of an incident beam from a third port.   
     
     
       2. The device according to claim 1 wherein the means for nonreciprocal rotation comprises a Faraday rotator and a half-wave plate. 
     
     
       3. The device according to claim 1 wherein the thickness of the second plate is approximately twice the thickness of the first plate. 
     
     
       4. The device according to claim 1 wherein the reflecting element comprises a prism having two surfaces at ninety degrees and a third surface at forty-five degrees to the other two surfaces, and the slotted portion is formed through one of the two surfaces and the third surface. 
     
     
       5. The device according to claim 1 wherein the circulator includes at least four ports and further comprises: a second reflecting element with a slotted portion disposed between the first port and the first plate; and a fourth birefringent plate disposed between the reflecting element and the fourth port. 
     
     
       6. The device according to claim 1 wherein the birefringent plates comprise rutile, and the rotation means includes a Faraday rotator comprising an yttrium iron garnet crystal and a half-wave plate comprising quartz. 
     
     
       7. The device according to claim 1 wherein the birefringent plates each have optical axes in a plane at an angle of ±48 degrees with respect to the horizontal in the direction of light incident from port 1. 
     
     
       8. An optical circulator having at least three ports comprising: a first rectangular birefringent plate disposed at a first port and oriented in order to separate a light beam incident at that port into two beams having orthogonal directions of polarization;   a second rectangular birefringent plate having a thickness greater than said first plate and disposed at a second port with an orientation so as to recombine the two beams;   means disposed between the plates for nonreciprocal rotation of the directions of polarization of the beams comprising a Faraday rotator and a half-wave plate;   a third rectangular birefringent plate disposed between the rotation means and the second plate and oriented in order to further separate the two beams; and   a prism having two surfaces at right angles, each of which is adjacent to one of the second and third plates, and a third surface at forty-five degrees to the other two surfaces, which third surface is adjacent to a third port, said third surface and the surface adjacent to said third plate having a slotted portion formed therethrough so that the beams from the third plate are deflected by said third surface while light incident from the third port passes through the slotted portion.